Polyvinylchloride (PVC) is a technically and economically very important polymer and is used as soft PVC and hard PVC in a large number of applications. For soft PVC plasticisers are often used. Important applications include amongst others electrical isolation materials around cables, flooring materials, various coating applications and shoe soles.
Plasticisers are used in various polymers to enhance the flexibility. By virtue hereof the possibilities and applications of these polymers are substantially enhanced. Plasticisers usually are liquids that can be used in various technical processes. They are optimized for various polymers. More in particular the polarity of a plasticiser should match with the polarity of the polymer to obtain a good interaction with the highest efficiency and low migration. Plasticisers are used in various polymers, among which the most important are: polyvinylchloride, polyamide, polar rubbers and polyurethane. Also in PVC plasticisers are often used. An important field of applications are those whereby the PVC is suspended in the plasticiser and a plastisole is being formed that can be coated on a substrate. On this substrate heating it above the so-called jellifying temperature then jellifies the PVC layer. For this application good and quick jellifying plasticisers (e.g. fast fusers) are used. They lower the jellifying temperature of PVC. Traditional examples of these products are for example BBP (benzyl-butyl-phthalate) or ethyleneglycol-propyleneglycol di-benzoate.
Plasticisers for polymers are usually phtallic acid esters. Still today about 80% of the plasticisers for PVC are phthalates. They give the product an enhanced flexibility in a great number of applications. The plasticiser molecules are positioned among the polymer chains and enhance the mobility of the polymer chains and lower the glass transition temperature. Plasticisers have the ability to couple substantially improved process properties to a high flexibility of the end product. The working principle of the above plasticisers relate to the so-called external plasticisers.
These are products that additionally are added to polymers after their preparation; their plasticiser function is a result of a physical interaction with the polymer molecules, as described above.
There also exist internal or inside plasticisers. These are products that during the preparation of the polymers in the polymer chain are incorporated as copolymers and by virtue hereof give the end product a flexible property. The present invention only relates to so-called external plasticisers.
Esters are the most interesting class of plasticisers. Apart from the earlier mentioned phthalate esters, also amongst others the following plasticisers are often found in actual applications: adipates, sebacates, maleates, gluterates, trimellitates, citrates, benzoates, sulfonamides, phosphate-esters, glycoletheresters, terephthalates, cyclohexane-dicarboxylates and polymeric plasticisers. Recently more plasticisers are being developed and used, partly or entirely synthesized from biological raw materials. Examples of the latter are: citrate esters, epoxied oils or fatty acid esters, acetylated monoglycerides.
The most often used plasticisers are di-octyl-phthalate (DOP), di-2-ethylhexylphtalate (DEHP), di-isononylphtalate (DiNP), di-isodecylphthalate (DiDP), di-undecylphthalate (DiUP), di-2-ethylhexyladipate (DOA), acetyl-tributylcitrate (ATBC), di-isononyl-cyclohexane-1,2-dicarboxylate (DINCH), di-octyl-terephthalate (DOTP).
Also esters of succinic acid or succinates are known as potential plasticisers.
In most applications the di-esters are used, that result from the esterification of succinic acid with a single aliphatic alcohol (both alkoxy groups being the same).
STUART et all. have published an article on this subject ‘Poly (vinyl chloride) plasticised with succinate esters: synthesis and characterization’, published in Polym. Bull. (2010). In this case they used di-octyl-succinate (DOSu), di-hexyl-succinate (DHSu), di-butyl-succinate (DBSu) and di-ethyl-succinate (DESu). They observed various parameters such as infrared absorption and glass transition temperature and compared these results with di-octyl-phthalate (DOP). However the plasticisers that had been tested were characterised by a substantially higher volatility (VOC, volatile organic compound) compared to the standard plasticisers as phthalates and comparable adipates. So from a commercial and technical point of view they are of less relevancy. From test results performed by the present inventors it appears that di-2-ethylhexyl-succinate (DEHSu) is approximately twice as volatile as the comparable adipate ester, di-2-ethylhexyl-adipate (DEHA).
Tests performed by the present inventors also revealed that the normal aliphatic di-esters of succinic acid with 2 equal alkoxygroups either exhibit a too high volatility or an insufficient jellifying property as desired for typical applications.
In the known state of the art plasticisers are also described that can be obtained by esterification of succinic acid with a mixture of two different types of alcohols. In this way a mixture can be obtained of products comprising an ester of succinic acid with two different alkoxygroups.
Reference is made for example to the British patent specification Nr. 1,071,525, filed Aug. 31, 1964, calling upon a priority of a Swiss application filed Aug. 29, 1963. This patent has been published on Jun. 7, 1967, applicant is Lonza Ltd.
This application describes the plasticising effect on amongst others vinyl chloride polymers with low-molecular weight esters based on succinic acid compounds. As an example on page 2, left column, line 43, is mentioned lauryloxy-propylene-succinoyldioxy-propylene acetate.
This is a mixed ester of succinic acid with at both sides an alkyl rest, at the one side with 15 carbon atoms, at the other side with 5 carbon atoms.
Nowhere in the text the use of these compounds in plastisoles has been described.
Reference is also made to the U.S. Pat. No. 3,483,247, filed on Nov. 9, 1964, published and issued on Dec. 9, 1969, in the name of Monsanto Co., St. Louis, USA.
This application describes on column 1, lines 30-32 the preparation of an aliphatic benzyl ester, being an ester comprising on the one side a benzyl group and on the other side an aliphatic group.
Column 4, line 1-2, cites the use of these products as plasticiser in vinyl halide plastics.
Column 4, line 45, cites succinic anhydride as starting raw material.
Column 4, lines 71 and following cite examples of monohydroxy aliphatic alcohols.
Amongst others are cited 2-ethylhexyl alcohol, nonyl alcohol, decyl alcohol, dodecyl alcohol, tridecyl alcohol, . . . .
Specific mixed esters based on succinic acid are mentioned in column 7, lines 33-35: benzyl methyl/ethyl/isohexyl succinates, so a mixed ester with benzyl on the one side, and on the other side an alkyl with 1, 2, 6 carbon atoms, and also: benzyl 2 ethylhexyl, so with 8 carbon atoms, and further benzyl decyl succinate: so with 10 carbon atoms; and further also benzyl tridecyl succinate . . . so with 13 carbon atoms. The text does not mention any specific properties of the cited succinate plasticisers.
Further reference is being made to the U.S. Pat. No. 3,148,207, filed on Apr. 14, 1958, issued on Sep. 8, 1964, in the name of Monsanto Co., Delaware, USA. This application describes the use of plasticisers for polyvinylchloride (column 1, lines 16-17).
Column 2 cites a long enumeration of carbonic acids that upon esterification may serve as plasticisers. Line 26 mentions succinic acid.
Column 3, line 72 mentions the use of mixed esters.
In example 14 on column 8 the preparation of a symmetric succinic acid ester has been described, namely dioctyldecyl succinate.
Further reference is made to the Japanese patent publication with publication number 2003 082158.
This application is published on Mar. 19, 2003, applicant is Arakawa Chem. Ind. Co Ltd., Japan.
This application mentions the use of a very specific succinate, namely on the basis of ditetrahydrofurfuryl as plasticiser for biologically degradable polyesters.
Further reference is being made to the European Patent Application Nr. 0013 167, filed on Dec. 21, 1979, calling upon a priority of a US application filed on Dec. 26, 1978, published on Jul. 9, 1980. This application has been filed in the name of Monsanto Company, St. Louis, Mo., USA.
This application describes on page. 1, lines 5-6, vinyl chloride polymer films and plastisoles for use in the preparation of such films.
On page 2, first two lines, plasticisers are mentioned for the preparation of such plastisoles, being esters of carboxylic acids, such as for example alkyl benzyl phthalates. On page. 3, lines 16-18, the use of a plasticising amount of for example a di-ester is mentioned, selected from alkyl benzyl succinates.
On pag. 6, lines 7-18, these alkyl benzyl succinates are further discussed.
Here is mentioned that the di-esters of succinic acid are formed by linking a benzyl radical directly to the one carboxyl group, and an alkyl radical to the other carboxyl group of the acid, for example succinic acid.
On line 18, in decreasing sequence of preference, examples of such alkyl compounds are enumerated, six in total.
These relate to isobutyl, n-butyl, sec-butyl, neopentyl, isopropyl and isoamyl respectively.
The alkyl compounds enumerated here thus have 4, 4, 4, 5, 3 and 5 carbon atoms.